Abstract/Project Summary The suicide rate among young adults aged 18-25 has risen to the highest level in more than 30 years, yet our ability to accurately predict suicide attempts remains limited to distal, static risk factors. There is an urgent need for research to identify ways to assess who is most at risk for suicide in the near future, consistent with Aspirational Goal 3 of the National Action Alliance?s Prioritized Research Agenda. Accordingly, the overarching goal of this R01 from an Early Stage Investigator is to improve our ability to identify specific near-term, dynamic within-person processes that predict acute increases in a vulnerable individual?s risk for suicide. Social processes related to affiliation and attachment (e.g., social rejection or exclusion), as well as painful and provocative events (PPE; e.g., violent trauma and self-injury), are well-known distal risk factors for suicide. However, the role of dynamic cognitive-affective and biological responses to experiences of rejection for predicting near-term suicide risk in any individual is poorly understood. In addition, it is not known how the influence of rejection-related processes on near-term suicide risk may vary as a function of distal risk factors such as exposure to PPE. The current application outlines a multimethod intensive longitudinal study to examine dynamic affective and physiological responses to rejection as near-term risk factors for temporal fluctuations in suicidal thoughts and behaviors (STB) over the course of hours to days, weeks, and months. We will also examine exposure to PPE as a moderator that amplifies intraindividual reactivity to social rejection, thereby further increasing suicide risk. Participants will include a diagnostically diverse clinical sample of 150 young adult men and women (ages 18 to 35) with clinically significant STB in the past 4 months. Multimodal assessments at baseline will include a 21-day random and event-based ecological momentary assessment (EMA) protocol; laboratory paradigms with psychophysiological measures, self-reports, and assessment of implicit suicide-related cognition; and interviews using timeline follow-back (TLFB) methods. Assessments at 4-month intervals over the course of 12 months will include repeated laboratory tasks, physiological and implicit assessments, self-reports, and TLFB interviews to assess changes in responses to rejection, PPE, and STB over time. The proposed project has three specific aims: (1) Examine multimodal measures of within- individual affective and physiological responses to rejection as near-term, prospective predictors of within- person fluctuations in STB over time; (2) Examine exposure to PPE as between-persons distal moderators of within-person processes leading to near-term increases in STB at the individual level; and (3) Apply machine learning techniques to identify combinations of multiple time-varying within-person processes and static between-person differences that are most predictive of suicide risk over time. Results of this study will lead to advances in suicide risk assessment, identification of novel points of intervention, and development of personalized interventions to prevent suicide attempts among vulnerable individuals.